FREMANTLE defender Zac Dawson says becoming a senior player crept up on him but he feels good about entering his second season in purple with more responsibility on his shoulders.

Dawson, who crossed from St Kilda at the end of 2011, was a key player in his first season at Fremantle, highlighting his importance by keeping Geelong forward Tom Hawkins goalless in the elimination final at the MCG.

After playing just 14 games in his first three years at Hawthorn, the key defender said he still felt young in football terms, entering the new season with 85 games under his belt.

However, his stature at Fremantle has grown quickly and he will again be relied on to shutdown the opposition's power forwards, alongside veteran Luke McPharlin.        

"I'm getting old. I turned 27 over the weekend so this will be my 10th year coming up," Dawson said on Tuesday.

"I just started to kick myself, over the weekend everyone was saying, 'You're 27, you're getting close to 30'. It doesn't feel like that.

"I only started playing genuine AFL footy probably four years ago when I first got to St Kilda, so it only feels like I've been playing proper AFL for four years.

"To be 27 and feel like that, I feel good."

Fremantle faces a challenge this pre-season to replace retired defender Adam McPhee, who played an important role in the back six last season, shutting down small forwards and adding hardness.

Garrick Ibbotson, Paul Duffield and Lee Spurr are all working to fill the void and Dawson said there could be a backline vacancy for a young player.

"He (McPhee) played a pretty good year last year, so I think one of the young boys is going to have to step up," Dawson said.

"So far Garrick Ibbotson has been playing that sort of role, and Paul Duffield. They're going to have to add that hard edge, which he gave us.

"Someone's obviously going to be fighting for that spot, it's a pretty coveted spot, and the boys will be working hard for it."

Dawson said the Fremantle back six was a tight knit group and they had worked hard over the pre-season with an expectation to lift their performances in 2013.

Personally, the former Saint expected to play the majority of the NAB Cup after making a slow start to his pre-season.

"I had a pretty easy run before Christmas so up until the season now I'll probably have to play most minutes and get my fitness through the matches," he said.

"I'd rather get my fitness through playing games than running laps any day of the week, so it's good for me.

"The last couple of weeks I've been back in full training and starting to feel really good.

"Over the weekend I got a bit more match fitness and I'm starting to come good now."

Zac Dawson is a defender in NAB AFL Fantasy. He averaged 34.88 points in 2012. Register your team at our AFL Fantasy Hub.

Nathan Schmook is a reporter for AFL Media. Follow him on Twitter: @AFL_Nathan